How can I separate my scene into render layers to render my animation faster in Cycles?
So here's what I came up with:



Basically, if the shot's fixed, and the camera doesn't move I pre-render the BG and the FG (The first 2 image inputs).
Then, with render layers:

Animation Render Layer: I put everything that has to be animated or interacts with the animation on visible layers and the rest just influencing those objects, but NOT VISIBLE.

Shadows Render Layer: Has a basic ground plane to receive the shadows with Shadows and AO render passes enabled. Here, I EXCLUDE the BG and FG.


Then, the Shadows Layer needs a Dilute/Erode node

And voilá! From about 1-2 hours of render time to 5 minutes per frame.
Again, this requires fixed shots.

Still...I'm no compositor wiz and this surely needs improving! For example, the Shadow Pass simply doesn't work...why is it there in the first place. Only the AO works. But it would make sense that the Shadows pass is what enables the shadow only calculation in the first place.